manucordier
17th Apr 2012, 12:54
Hello,
I am having a hard time to find a footage on youtube (or elsewhere) which demonstrates the position of aerodynamic center (AC, 25%MAC) and neutral point (NP).
We can read in many books on aerodynamics that while the angle of attack (AoA) is changing on the wing taken alone, the pitching moment of the wing about the AC remains constant (thus AC is our pivot in this experience).
The reason for this, according to what we can read in the books, is because the lift (L) is effectively applied at the center of pressure (CP, which position changes for different AoA) while the change in lift (Delta L) takes place at the AC (which position is a constant: 25%MAC). Moreover, we know that any change in a force applied on the pivot (AC) of a body does not modify its total moment.
I suppose this could be easily shown in a wind tunnel by setting a pin through the wing at 25% of the MAC. Then you increase the angle of attack of the relative airflow. During the change in AoA, the pitching moment should remain constant. However once the variation of AoA comes to an end and the AoA remains constant, all the lift takes effectively place at the CP. So the pitching moment must change and generate a pitch up or down (depending on the position of the CG compared to that of the CP).
I want to see that in a wind tunnel.
The same goes for the Neutral Point, because the NP is, in some way, the AC of the whole airplane.
Could anyone provide me with a document (text, photos, movie) showing that experience in a wind tunnel.
Thank you very much.
I am having a hard time to find a footage on youtube (or elsewhere) which demonstrates the position of aerodynamic center (AC, 25%MAC) and neutral point (NP).
We can read in many books on aerodynamics that while the angle of attack (AoA) is changing on the wing taken alone, the pitching moment of the wing about the AC remains constant (thus AC is our pivot in this experience).
The reason for this, according to what we can read in the books, is because the lift (L) is effectively applied at the center of pressure (CP, which position changes for different AoA) while the change in lift (Delta L) takes place at the AC (which position is a constant: 25%MAC). Moreover, we know that any change in a force applied on the pivot (AC) of a body does not modify its total moment.
I suppose this could be easily shown in a wind tunnel by setting a pin through the wing at 25% of the MAC. Then you increase the angle of attack of the relative airflow. During the change in AoA, the pitching moment should remain constant. However once the variation of AoA comes to an end and the AoA remains constant, all the lift takes effectively place at the CP. So the pitching moment must change and generate a pitch up or down (depending on the position of the CG compared to that of the CP).
I want to see that in a wind tunnel.
The same goes for the Neutral Point, because the NP is, in some way, the AC of the whole airplane.
Could anyone provide me with a document (text, photos, movie) showing that experience in a wind tunnel.
Thank you very much.